The present invention relates to a stair climbing wheelchair carrier designed to transport wheelchair users up and down stairs, and more particularly to a carrier that can be set and operated by the wheelchair users themselves.
A stair climbing wheelchair carrier shown, for example, in Japanese Examined Patent Publication No. Sho 64-7914 includes a motor-driven crawler device that travels up and down stairs, on which a front-facing wheelchair with a user on it is carried in a tilted back position. This carrier does not allow the wheelchair user to set the wheelchair on the carrier without help from an operator or an assistant. This is against the recent trend of putting more weight on providing barrier free access to wheelchair users. Also, wheelchair users often have no physical impediments other than the walking disability. Therefore, a stair climbing wheelchair carrier which an unassisted wheelchair user can use as the user rests on the wheelchair needs to be developed.
Japanese Patent No. 2592669 shows a technique developed in response to this demand. Referring to FIG. 1A to FIG. 1C, this conventional wheelchair carrier includes a crawler drive unit J2 and a carrying unit J3. J1 represents a wheelchair. The crawler drive unit J2 drives crawler belts J20 with a motor to travel up and down stairs. The carrying unit J3 includes a support frame J30 for supporting the wheelchair J1 in a tilted back position, and anchoring hooks J31 that can engage with the back of the wheelchair J1 supported on the frame. The carrying unit J3 can be moved up and down relative to the crawler drive unit J2 by a lift mechanism J4. Male couplers J32 are pivoted on cross shafts J32a in the lower part of the support frame J30 of the carrying unit J3. To the cross shafts J32a are securely attached levers J32b which rotate with the male couplers J32. The levers J32b are connected to sliders J32d on guide bars J33 of the carrying unit J3 via connection rods J32c. The sliders J32d slide along the guide bars J33 with the rotation of the male couplers J32 relative to the support frame J30, to move cams J32e. 
To mount the wheelchair J1 on the carrying unit J3, the wheelchair J1 is moved backward from the state shown in FIG. 1A until the male couplers J32 mate with female couplers J11 formed on the wheelchair J1. The user (not shown) on the wheelchair J1 then holds a hand grip on the side of the support frame J30 and shifts the body weight to tilt the wheelchair J1 backwards until the wheelchair J1 touches the support frame J30. The wheelchair user then locks the backside of the wheelchair J1 on the support frame J30 with the anchoring hooks J31.
As the wheelchair J1 inclines backwards, the male couplers J32 rotate upward as shown in FIG. 1B, causing the sliders J32d and the cams J32e to slide on the guide bars J33. The cams J32e thereby rotate levers J21 attached to the crawler drive unit J2, causing a support wheel J23, which is pivoted on the same shaft as that of the levers J21, to make contact with the ground.
The user on the wheelchair J1 then operates a lever J41 of the lift mechanism J4 to lower the carrying unit J3 relative to the crawler drive unit J2 so that the crawler drive unit J2 is lifted up and the wheels J10 of the wheelchair J1 and the support wheel J23 make contact with the ground as shown in FIG. 1B to allow wheelchair movement.
When climbing up or down stairs with the crawler drive unit J2, the wheelchair user operates the lever J41 of the lift mechanism J4 to raise the carrying unit J3 relative to the crawler drive unit J2 so that the crawler drive unit J2 makes contact with the ground. When the carrying unit J3 is lifted up, the cams J32e are freed from the levers J21 and the support wheel J23 is retracted to a position inside the crawler drive unit J2. The support wheel J23 isbiased toward this retracted position. In this state, the crawler drive unit J2 is moved along the corners of the stairs K to climb up or down the stairs as shown in FIG. 1C.
This wheelchair carrier allows the wheelchair user to set the wheelchair J1 on the carrying unit J3 as the user remains on the wheelchair. Also, as the crawler drive unit J2 can be lifted up to bring the wheels J10 of the wheelchair J1 in contact with the ground, the user can move the wheelchair, for example, for making a small turn in a landing between the stairs, without an assistant.
With this structure of the conventional technique, the left and right wheels J10 of the wheelchair J1 bridge across the crawler drive unit J2 when the wheelchair J1 is mounted on the carrying unit J3, and therefore, when the wheelchair J1 is moved back from the state shown in FIG. 1A to be connected to the carrying unit J3, the coupling between the female couplers J11 and the male couplers J32 must be complete before the foot rest J12 (see FIG. 1A) of the wheelchair J1 touches the front end of the crawler drive unit J2. Meanwhile, since the front side of the crawler drive unit J2 always faces downwards during stair ascent and descent as shown in FIG. 1C, the carrying unit J3 must be located more backward of the center of gravity of the crawler drive unit J2 for stable movement on the stairs. This requires the wheelchair J1 to have more than a certain front to back length L (see FIG. 1A) to be connectable to the carrying unit J3 that is at the back of the crawler drive unit J2. However, athletic wheelchair users who have no physical impediments other than the walking disability tend to use wheelchairs with a small front to back length L for quick movability. Such small wheelchairs cannot be connected to the carrying unit J3 at the back of the crawler drive unit J2. The front to back length of the crawler drive unit could be shortened to solve this problem, but the stability during stair ascent and descent will then be sacrificed.